Operating refrigeration and air conditioning systems provide cooling by a change of state of a fluid refrigerant from a liquid state to a gaseous state in an evaporator coil. These systems cycle refrigerant in a closed-loop in which gaseous refrigerant leaving the evaporator coil is compressed by a motor driven compressor, returns to the liquid state in a condenser coil, then passes through an expansion valve, and then returns again to the evaporator coil.
Historically, refrigeration and air conditioning systems have used either mechanical bellows modules or expensive electronic modules for turning compressor motors on and off. Mechanical bellows type modules have been used for more than 70 years and are unsuitable for fine adjustments and accurate pressure sensing and precise compressor motor control. More expensive electronic control modules have been available for a few years but lack flexibility, programming advantages and accuracy.
U.S. Pat. No. 5,209,076 entitled “Control System for Preventing Compressor Damage in a Refrigeration System” discloses a microprocessor based monitoring device for refrigeration systems that uses sensors which detect various conditions at selected locations in a refrigeration system. Pressure and temperature sensors on the suction side of the refrigeration system's compressor provide information that allows computing the superheat. The microprocessor accepts entry of high and low safety limits for superheat for a specified refrigerant. If measured superheat falls outside of a programmed safety range, the microprocessor automatically shuts off the compressor motor, and generates an alarm signal to indicate that a problem has occurred.
Additional sensors monitor refrigeration system conditions such as the compressor discharge pressure and temperature, motor current and oil pressure. Similarly, the microprocessor accepts entry of safety limits for these conditions, and the microprocessor automatically shuts off the compressor motor, and generates an alarm signal if the refrigeration system is operating outside of a safe operating range with respect to any of the monitored conditions. To prevent aberrational or transient conditions from shutting down the refrigeration system, each monitored parameter is assigned a time-out interval throughout which an abnormal condition must persist before the microprocessor automatically shuts off the compressor motor.
The refrigeration system microprocessor based monitoring device can be incorporated as an original part of a refrigeration system, it can be added as an after market item permanently installed on an existing refrigeration system, or it can be used as a portable service tool which can be temporarily attached to a refrigeration system to obtain representative samples of the system's operating characteristics. The microprocessor based monitoring device can collect refrigeration system data over an extended time interval to identify any trends that may occur. For example, the disclosed monitoring device can sense each operating condition every ten minutes over a period of five days, and the data can be presented in the form of a graph or in any other meaningful format.
Preferably, the refrigeration system monitor includes a display such as a liquid crystal display, along with a key pad for entering program commands and functions and LED indicators for identifying alarm conditions. The data can be displayed on the monitor's LCD screen, printed out by a printer, or transmitted via a modem over telephone lines to allow displaying on a remote computer screen. Alternatively, the unit can be programmed to automatically dial a programmed telephone number if the refrigeration system should shut down so that appropriate personnel are alerted to the problem and can take whatever corrective action is indicated under the circumstances.